diff --git a/git-am.sh b/git-am.sh
index 5eec11d5f0..f35710cb50 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -327,6 +327,7 @@ split_patches () {
 		;;
 	hg)
 		this=0
+		test 0 -eq "$#" && set -- -
 		for hg in "$@"
 		do
 			this=$(( $this + 1 ))
@@ -353,7 +354,7 @@ split_patches () {
 					print "\n", $_ ;
 					$subject = 1;
 				}
-			' <"$hg" >"$dotest/$msgnum" || clean_abort
+			' -- "$hg" >"$dotest/$msgnum" || clean_abort
 		done
 		echo "$this" >"$dotest/last"
 		this=
diff --git a/t/t4150-am.sh b/t/t4150-am.sh
index 4beb4b3894..3ebafd9234 100755
--- a/t/t4150-am.sh
+++ b/t/t4150-am.sh
@@ -259,6 +259,16 @@ test_expect_success 'am applies hg patch' '
 	test_cmp_rev second^ HEAD^
 '
 
+test_expect_success 'am --patch-format=hg applies hg patch' '
+	rm -fr .git/rebase-apply &&
+	git checkout -f first &&
+	git am --patch-format=hg <patch1-hg.eml &&
+	test_path_is_missing .git/rebase-apply &&
+	git diff --exit-code second &&
+	test_cmp_rev second HEAD &&
+	test_cmp_rev second^ HEAD^
+'
+
 test_expect_success 'setup: new author and committer' '
 	GIT_AUTHOR_NAME="Another Thor" &&
 	GIT_AUTHOR_EMAIL="a.thor@example.com" &&